Telegraph switching system



M. E. GRlFFlNs 2,211,927

8 Sheets-Sheet l TELEGRAPH SWITCHING SYSTEM Filed Feb. 1'7, 1939 Aug. 20, 1940.

. INVENTOR ILTnrrs E. Griffin 5 ATTORNEY.

Allg. 20, 1940- E. GRIFFINs l 2,211,927

TELEGRAPH SWITCHING SYSTEM Filed Feb. 17, 1939 8 Sheets-Sheet 2 mum-i5 E. EMT-fins BY #Ama/v ATTORNEYS` M. E. GRn-'FINS 2,211,927

TELEGRAPH SWITCHING SYSTEM l Filed Feb. 17, 1959 8 Sheets-SheeI 3 www5 @wai U 9 Aug. 20, 1940.

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Aug. 20, 1940. M. E. GRIFFlNs TELEGRAPH SWITCHING SYSTEM A8 Sheets-Sheenl 5 Filed Feb. 17, 1959 ATTORNEYS.

Aug. 20, 1940- M. E. GRIFFlNs TELEGRAPH SWITCHING SYSTEM Filed Feb. 17, 1939 8 Sheets-Sheet 6 nchod@ GEEL www Q $3 mfbl we #WWW m n@ N www* HLM Q N n www m S l @mi S M IM: Y v .xp i. @QE l Ll IJ Jr n mkb b Sb M mwN/l l 4 @www N m E3 3 G3 S J w BY JWM; 4%5/ ATTORNEYS.

Aug. 20, 1940.

M. E. GRIFFINS TELEGRAPH swITcHING SYSTEM 8 -Sheets-Shee't 7 Filed Feb. 17, 1939 QON Aug. 20, 1940.A M. E. GRIFFlNs 2,211,927

TELEGRAPH SWITCHING SYSTEM l Filed Feb. 17, 1959 a s11m= t.,sheeL e l ATTORNEYS.

Patented Aug. 20,

UNITED STATES PATENT 'i oFEicE 'rELEGaarn swrrcmNG srs'rEM 1 Morris E. Grli'lins, Chicago, Ill., assignor to-Asso ciated Electric Laboratories, Inc., Chicago, lll., a corporation ofDelaware Application February 11,1939, serial No. 256,909

' 4s claims., (crus-z) with. An automatic selector switch is indivld ually connected in each telegraph line' at each station and has access to printing mechanism larranged in the station. Also dialing and transmitting mechanisms are arranged in each station whereby both dial and telegraphic impulses may be transmitted over each of-the telegraph lines at the station. Certain of the stations are associated with two or more of the telegraph lines and repeaters individually connected in the last-mentioned telegraph lines are arranged in the stations, which repeaters are accessible to the selector switches in the stations, whereby a communication connection may be established between a particular telegraph line and another telegraph line by causing the selector switch.

connected in the particular telegraph line to seize the repeater connected in the other telegraph line.

'I he selector switches connected in a given telegraph line are so connected and arranged that they are operative to corresponding positions in response to series of dialed impulses transmitted over vthe given 'telegraph line, each selector switch comprising normally effective im"- pulse responsive means for causing the selector switch to be selectively operated to a number of diierent positions. Each selector switch is operative to one or more particular positions which particular positions comprise non-corresponding positions of the selector switches in the system. When a selector switch is operated to a particular position it is switched through and seizes the printing line extending lto the printing mechanism or the trunk line extending to the repeater in the associated station. In the event a printing line is seized by the selector switch, the printing mechanism associated therewith is/rendered operative in response to subsequent telegraphic impulses transmitted over the telegraph line associated with the selector switch; and in the event a trunk line is seized bythe selector switch, the repeater associated therewith is rendered ef- 'sociated with theV telegraphline is released.

fective to repeat over the telegraph line connected thereto both dial and telegraphic impulses subsequently transmitted over the telegraph line associated with the selector switch. Also, upon switching through, the selector switch 5 transmits an answer-back signal over the telegraph line associated therewith. Furthermore, each selector switch comprises normally eilfective means responsive to the transmissionl of an answer-back signaltherto for causing the sel0v lector switch to be released, and ymeans controlled by the switching through of the selector switch for rendering ineective the last-mentioned means and the impulse responsive means in the selector switch. Moreover, a vrelease de- 15 vice is connected in each telegraph line at each station which is operative to transmit a release signal over the telegraph line; and. each selector switch comprises means responsive to the transmission of a release signal vthereto for causing 20 the selector switch to be released. Also each selector switch 1 comprises automatic release means which is responsive tov an incomplete operation of the selector switch, due to the transmission of an induction surge over the associ- 25 ated telegraph line caused by' lightning or the llke,.for causing the selector switch to operate and transmit a release signal over the associated telegraph line, whereby 'each selector switch as- 3 In setting up a communication connection beo tween ,two or more stations in a telegraph system of the character described, the operator in one of the stations rst actuates the dialing mechanism thereat in order to transmit first 35 predetermined series of dial impulses over a given telegraph' line, thereby to cause the selector switches associated with the given telegraph line to be operated to corresponding positions. This position oi one of the selector switches comprises a particular position thereof, thereby to cause the one selector switch to switch through and seize a printing line, trunk line, tc., over which dial or telegraphic impulses are to be transmitted. Upon switching through, the one 5 selector switch causes each of the other selector switches associated with the given telegraph line to be released. The operator then repeats the `the communication connection. After the. communicationconnection has been setup, the operator in the one station operates the transmitting mechanism, thereby to transmit telegraphic impulses over the communication connection whereupon the printing mechanisms associated with the printing lines included in the communication connection operate automatically to print the telegraphic message. 'I'he established connection may be released by the operator in the one stationupon operating the release device thereat in order to transmit a release signal over the communication connection whereupon each of the selector switches, which is switched through and included -in the communication connection, is released.

While reasonably satisfactory operation is obtained in a telegraph system of the type described, there are several objectionable features thereto. In the first place, each selector switch which has not been switched through and is included in an established communication connection tends to be operated by the telegraphic impulses transmitted over the communication connection. More particularly, at this time, the selector switch is released and the impulse responsive means therein is effective to respond to dial impulses, thereby to cause theselector switch to be operated. Although telegraphic impulses are considerably different from dial impulses and are not ordinarily effective to cause the selector switch to be operated, this difference resides only in the relatively high rate of the telegraphic impulses; and occasionally a telegraphic impulse is transmitted over the communication connection which `is sufficiently similar to a dial impulse to cause the selector switch to be partially operated. Moreover, lightning surges and the like occasionally cause impulses to be transmitted over the communication connection which closely resemble dial impulses, thereby to cause the selector switch to be partially operated. When the selector switch is partially operated, the automatic release means therein responds to transmit a release signal over the communication connection which results in the automatic release of the established communication connection prior to the completion of the telegraphic message and against the will of the operator.

Accordingly, it is an object of the present invention to provide, in a telegraph system of the type described, an arrangement for rendering non-responsive to dial impulses each of the selector switches included in an established connection prior to the transmission of telegraphic impulses over the established communication connection.

Another object of the invention is to provide, in a telegraph system of. the type described, a number of selector switches associated with the telegraph lines therein which are so connected and arranged that they are operative to corresponding positions, including switching and lockout positions, in response to series of dial impulses, each of the selector switches being so connected and arranged that it is rendered nonresponsive to further dial impulses when it is operated to a switching position or to a lock-out position.

A further object of the invention is to provide, in a telegraph system of the type described including two stations associated with a group of telegraph lines and another station associated with a given telegraph line, a selector switch of the trunk hunting type individually associated with the given telegraph line and having access to each telegraph line in the group, whereby a aai 1,927

communication connection may be routed between the other station' and either one oi the two stations by way of the given telegraph line and an idle one of the telegraph lines in the group.

A further object of the invention is to provide, in a telegraph system of the type described including nrst stations associated with a first group or telegraph lines end second stations associated with a second group of telegraph lines, selector switches of the trunk hunting type individually associated with the telegraph lines in each of the groups, whereby a communication connection may be routed in either direction between eitherV one of the rst stations and either one of the second stations by way of an idle telegraph line .in the first group and an idle telegraph line in the second group.

A further object of. the invention is to provide,

in a telegraph system of the type described, an improved arrangement utilizing a selector switch associated with a loop circuit and a repeater for operatively associating with a telegraph line a printing mechanism accessible to the selector switch.

A further object of the invention is to provide, in a telegraph system of the type described, an improved arrangement utilizing a selector switch associated with' a loop circuit and a repeater for operatively associating with a telegraph line an- I other telegraph line having a potential of a given polarity impressed thereupon and accessible to the selector switch.

The features of the present invention are illustrated as being incorporated in a telegraph system comprising first terminal stations associated with a iirst group of telegraph lines, second terminal stations associated with a second group of telegraph lines, a third terminal station associated with a' third telegraph line, and a central switching station commonly associated with each of the telegraph lines in the ilrst and second groups and with the third telegraph line. Also one or more wayside stations may be associated with each of the telegraph lines. In each of the terminal and wayside stations and in the central switching station there are provided dialing and transmitting mechanisms operative to transmit dial and teiegraphic impulses, respectively, over any one of. the telegraph lines at the station. Also in each of the stations mentioned there is printing mechanism which is operative in response to telegraphic impulses transmitted thereto to print the telegraphic message, a group of printing mechanisms being provided in at least the central switching station. In each of the stations a selector switch is individually associated with each telegraph line thereat, each selector switch -having access to the printing mechanism at the station.

y Each of the telegraph lines in the first and second groups is connected to a source of current and is normally arranged in a closed circuit; while the third telegraph line has a potential of a predetermined polarity impressed upon the end thereof in the third terminal station and is normally arranged in an open circuit.

In accordance with one feature of the invention, the selector switches in the central switching station are arranged in first and second groups, the selector switches in the flrst group being individually associated with corresponding ones of the telegraph lines in the first group, and the selector switches in the second group being individually associated with corresponding ones group.

of the telegraph lines in the second group. yMore particularly, each of the selector switches in the first group is provided with a control network connected i-n. 'a loop circuit individually thereto, the loop circuit being normally connected to a local source of current andbeing operatively asgroup., Also, there-is provided in the central switching station a rst group of trunk lines individually extending to corresponding ones oi the selector switches in the first group and va second group of trunk lines individuallyextending to corresponding ones'oi the selector switches in the second group, each oi the trunk lines in the iirst group being accessible to each of the selectorswitches in the second group, and each of'the trunk lines in the second group being ac.I cessible to each of the selector switches in the first group.

Each of the selector switches in the first and second groups is of the trunk hunting type, each of the selector switches in the first group being operative in response to a predetermined operation thereof to select a trunk line in the second group extending to a selector switch in the second group associated with an idle telegraph line in the second group and each of the selector switches in the second group being operative in response to a predetermined operation thereof to select a trunk line in the first group extending to a selector switch in the iirst group associated with an idle telegraph line in the iirst group. Means is provided in each of the selector switches in the first group which is operative when the selector switch operates to seize the trunk line in the second group to'disconnect the loop circuit from the local source of current and for causing the selector switch to switch through, thereby to connect the control network of the selector switch in series with the trunk line in the second group. Means is provided in each of the selector switches in the second group which is responsive to the seizure of the trunk line in the second group extending thereto for causing the selector switch to operate and connect the trunk line in series with the control network thereof, whereupon subsequent impulses transmitted over the control network of the previouslymentioned selector switch in the iirst group are also transmitted over the control network of the last-mentioned c selector switch in the second group and over the corresponding telegraph line in the second group. Means is provided in each of the selector switches in the second group which is operative when the selector switch operates to seize the trunk linein the first group to cause the selector switch to switch through, thereby to connect the control network of the selector switch in series with the trunk line in the rst group. Means is provided in each of the selector switches in the rst group which is responsive to the seizure ofthe trunk line in the first group extending thereto for disconnecting the local source of current from the loop circuit associated with the selector switch and ,for causing the selector switch to operate and connect the trunk line in series with the control network thereof, whereupon subsequent impulses transmitted/ over the control network of the previously mentioned selector switch in the second sroup are also transmitted over 'the control network of the last-mentioned selector switch in the nrst group and over the corresponding telegraph line in the nrst group.

In accordance with another feature oi' the invention, each of the selector'switches in the iirst and second groups is operative to select an idle printing mechanism Vin the group of printing mechanisms in the .central switching station. More particularly, means is provided in each of the selector switches in theiirst group for causing the selector switch to operate as a trunk hunting selector switch and seize a printing line extending to an idle printing mechanism in the censelector switch are transmitted over the seized printing line, thereby to cause the printing mechanism associated' therewith to operate and print the telegraphlc message. Also means is provided in each of the selector switches in the second group for causing the selector switch to operate as a trunk hunting selector switch and seize a printing line extending to an idle printing mechv anism in the central switching station. Also means is provided in each of the selector switches in they second group which is responsive to the seizure of the idle printing line for causing the selector switch to @switch through and connect the idle printing line in series with the control network thereof, wherebyrsubsequent telegraphic impulses transmitted over the control network of the last-mentioned selector switch are transmitted over the seized printing line, thereby to cause the printing mechanism associated therewith to operate and print the telegraphic message.

At least one of theselector switches in each of the rst and second groups is operative to select the third telegraph line. More particularly, means is provided in the one selector switch in the first group which is operative to cause the last-mentioned selector switch to seize the third telegraph line. Also means is provided in the last-mentioned selector switch and responsive to the seizure of the third telegraph line for disconnecting the local source of current from the loop circuit associated with the selector switch and for causing the selector switch to switch transmitted over the third telegraph line. Means is provided in the one selector switch in the second group. which is operative to cause the- Also it is noted that the impulses transmitted over the last-mentioned trunk line are repeated by the last-mentioned repeater over the third telegraph line.

Means'is provided in each of certain ones of the selector switches in the first and second groups for positively preventing these selector switches from having access to the third telegraph line. More particularly, means is provided in each4 of the last-mentioned selector switches which is operative in response to the operation thereof to a givenposition corresponding to the third telegraph line for causing the selector switch to switch through and then automatically to be released.

In accordance with another feature of the invention, the selector switches associated with a given telegraph line are so connected and arranged that they are operative to corresponding positions in response to series of impulses transmitted over the given telegraph line. Each of the selector switches is also operative to first and second particular positions, the first particular positions being non-corresponding positions of the selector switches and the second particular positions being corresponding positions of the selector switches. Means is provided in each of the selector switches which is responsive .to the operation thereof to its first particular position for causing the selector switch to switch through and perform a given switching function to extend a connection; and means is provided in each of the selector switches which is responsive to the operation thereof-to its second particular position for causing the selector switch to switch through without performing the given switching function. Normally effective impulse responsive means is provided in each of the selector switches to cause the selector switch to be selectively operated; and normally effective release means re-v sponsive to the transmission of an answer-back signal thereto is provided in each of the selector switches for causing the selector switch to beI released. Means is provided in each of the selector switches which is controlled when the selector switch switches through for transmitting an answer-back signal over the control network thereof and for rendering ineffective the release means in the selector switch. Also means is provided in each of the selector switches which is operative in response to the seizure of a busy telegraph line, trunk line or printing line by the selector switch to cause a busy signal to be transmitted over the control network of the selector switch. Furthermore, timing means is incorporated in each of the selector switches which is responsive to an incomplete operation of the selector switch for causing a release signal to be transmitted over the control network of the selector switch. Also a release device is provided in each of the stations which is operative to transmit a release signal over any one of the telegraph lines thereat. Finally, means is provided in each of the selector switches which is responsive to the transmission of a release signal over the control network of the selector switch to render effective the release means in the selector switch, whereby the selector switch is released. 4 Further features of the invention pertain to the particular arrangement of the circuit elements thereof whereby the above-outlined and additional features are attained.

The novel features believed to be characteristic of the invention, both as to its organization and method of operation, together with further ob- Description of the apparatus'incmporated in the telegraph system Referring now more particularly to Fig. .1 of the drawings, the telegraph system there illustrated comprises two terminal stations N and S lhaving a number of telegraph lines, including the telegraph lines |0| and |02, extending therebetween, two terminal stations E and W having a number of telegraph lines, including the telegraph lines 50| and 502. extending therebetween, a central switching station C commonly associated with the telegraph lines |0|, |02, 50| and 502, and a terminal station X having a telegraph line 60| extending to the central switching station C. Also, a number of wayside stations, not shown, may be associated with each of the telegraph lines |0|, |02, 50|, 502 and 50|. Preferably, each of the telegraph lines is of the single conductor 4type and the terminal end thereof has impressed thereon in the associated terminal stations a predetermined battery potential. More particularly, the terminal ends of the telegraph lines |0| and |02 terminating at the station N have positive battery potential impressed thereupon; the terminal ends of the telegraph lines 0| and |02 terminating at the station S have negative battery potential impressed thereupon; the terminal ends of the telegraph lines 50| and 502 terminating at the station E have positive battery potential impressed thereupon; the terminal ends of the telegraph lines 50| and 502 terminating at the station W have negative battery potential thereupon; the terminal end of the telegraph line 60| terminating at the station X has positive battery potential impressed thereupon; and the terminal end of the telegraph line 60| terminating at the central switching station C is adapted to'have negative battery potential impressed thereupon, the telegraph line 50| being included in a normally open circuit. A repeater included in the central switching station C' is individually associated with each of the telegraph lines extending between the stations N and S. the repeater |00 being individually associated with the telegraph line |0| and the repeater |05 being individually associated with the telegraph line |02. Also a repeater 510 is individually associated with the telegraph line 60| for a purpose more fully explained subsequently.

A selector switch included in each of the terminal and wayside stations is individually associated with each of the telegraph lines extending thereto. Similarly, a selector switch included in the central switching station C is individually associated with each of the telegraph lines extending between the stations E and W, the selector switch 520 being individually associated with the telegraph line 502 extending therebetween, and the selector switch '|00 being individually associated with the telegraph line 50| extending therebetween. Also. a selector switch included in the central switching station C is individually associated with each v of the repeaters individually associated with theincluded in each of the stations and are individually included in each of the telegraph lines extending thereto or are disassociated with the telegraph lines extending thereto, as desired. When the transmitting and printing mechanisms are disassociated with the telegraph lines extending to a station, the printing mechanisms are arranged to be selected by the selector number of unitary dial-transmitting-printlng mechanisms, including the mechanism |60, are arranged in the central switching station C. It is noted that the printing mechanisms 490, 491 and 498 included in the central switching station C are so connected and arranged that they are individually accessible to the selector switches 300, 5|0, 520 and 100 at the central switching station C. More particularly, these printing mechanisms are so connected and arranged that the selector switches 300, 5|0, 520 and 100 are operative to select an idle one of these printing mechanisms when a predetermined series of dgits is dialed into one of these selector switches, in a manner more fully described subsequently. Also, it is noted that a jack is arranged in each of the telegraph lines |02, 50| and 502 extending to the central switching station C and that each of the dial-transmitting-printing mechanisms in the central switching station C is provided with a plug, whereby the dial-transmitting-printing mechanisms included in theA central switching station C may beindividually and selectively included in the telegraph lines extending thereto by selectively inserting the plugs into the jacks mentioned. `More particularly, the jacks |03, |04,`503 and 504 are individually included in the Atelegraph lines |0|, |02, 50| and 502, respectively; and the dialtransmitting-printing mechanism |60 is provided with a plug |05.

1f. wm be observed that4 the 1m1-swimmingprinting mechanisms 8|0 and 000 included in the station S are arranged directly in the telegraph lines |0| and 02, respectively, extending thereto.

Each of the selector switches included in the central switching station C is so connected andarranged that it has access to each of the printing mechanisms 490, 491 and 498 included in the central switching station C and is operative to search this group of printing mechanisms for an idle printing mechanism therein, as previously noted. Also, the, selector switches 300 and |0 individually associated with the repeaters |00 and |05, respectively, are so connected and arranged that they have access to each of the selector switches 520 and 100 individuallyassociated with the telegraph lines 502v and 50|, respectively, and are operative to search for an idle one of the two last-mentioned selectors. Similarly, each of the selector switches 520and 100 individually associated with the telegraph lines 502 and 50|, respectively, are so connected and arranged that they have access to each of` the selector switches 300 and 5|0 individually associated with the repeaters |00 and |05- and are operative to search for an idle one .of the two last-mentioned selector switches.Also, the selector switches 300 and 520 have access to the telegraph line 60|; while each of the selector switches 5| 0 and 100 is provided with an arrangementindivi'dual thereto for positively preventing s the associated selector switch from having access to the telegraph line 60| in a manner more fully described subsequently. From the foregoing description of the connection and arrangement of the selector switches 300, 5|0, 520 and 100 included in the central switching station C, it will be understood that each of the telegraph lines 50| and 502 may be individually connected to.

either one of the telegraph lines |0| and |02; each of the telegraph lines |0| and |02 may. be

individually connected to eitherone of the telel stood that each of the dial-transmitting-printing mechanisms included in the Icentral switching station C may be individually connected directly into the telegraph lines |0|, |02, 50| and 502. by way of the associated plugs and jacks previously mentioned; while each of the last-mentioned mechanisms may be individually connected to the telegraph line 60| by way of the telegraph line 502 and the selector switch 520 associated therewith or by way of the telegraph line |0|, the repeater |00 individually associated with the telegraph line |0| and the selector switch 300 individually associated with the repeater |00, in a manner more fully described subsequently. Accordingly, each of the terminal stations N, S, E and W, each of the wayside stations associated with the telegraph lines |0|, |02, 50| and 502, and the central switching station C may originate and receive telegraphic calls; while the terminal station X and the wayside stations associated with the telegraph line 60| may not originate telegraphic calls. y

Each ofthe selector switches included in the terminal, wayside and central switching stations may be substantially identical to the selector switches 300 and 100 included in the central switching station C and illustrated in Figs. 3, 4, and 7, 6, respectively. The selector switch 300 comprises a Strowger switching'mechanism 480 and a minor switch 390 comprising a portion position.

of a timing arrangement, described 'in detail hereinafter. The Strowger mechanism 466 includes a bank of fixed contacts arranged in ten vertical levels, each level including ten radially disposed contact sets. each contact set being adapted to terminate a telegraph or printing mechanism line extending thereto, and a wiper' mechanism 400 are a number of sets of switch Springs S661, S666, S466, S466, S466 and S461 which are actuated by the various movements.l

ef the carriage thereof. More particularly, the sets of switch springs S301, S366 and S466 are actuated when the carriage of the Strowger mechanism 460 is moved vertically away from its normal position; the set of switch springs S466 is actuated when the carriage is moved vertically to a predetermined level; and the sets of switch springs S466 and S461 are actuated when the carriage is moved vertically to a different predetermined level. The minor switch 390 includes a rotatable wiper 66| and an associated radially bank 302 comprising a number adapted to terminate a group of control lconductors for a purpose more fully describedv mbsequently. Also, the minor switch366 includes a rotary magnet M393 for rotating the wiper-.36| across the associated contact bank 6922and^a release magnet M394 for releasing the wiper 60|' and'returning it to its normal position. `Also,a setof switch springs S395 is associated with the minor switch 390 which is actuated by the movement of the wiper 39| away from its normal Furthermore, the selector switch'660 comprises a group of relays and their` control and controlled circuits, this gropoi' relays including a line relay R3|0, a hold relay R626, a test relay R450, a busy relay R460, a switch-through relay R410, and a number of control relays R660, R646, R350, R360, R310, R360,R366, R400, R4|6. R420, R440 and R460. Also, 'it is noted that the selector switch 300 is so connectedand arranged that it is adapted to operate as a trunk hunting switch to search for an idle line in a particular group of lines and is individually associated with the repeater |00 by way of the loop circuit 30| including the conductors C302 and C306. Finally, it is noted that a supervisory lamp L366 is individually associated with the selector switch 366 for a purpose more fully described subsequently.

In general, the selector switchl is connected.

and arranged in a manner substantially identical to the selector switch 300 and comprises a Strowger switching mechanism 600 and a minor switch comprising a portion of a-timing arrangement, described in detail hereinafter. The Strowger mechanism 660 is identical tothe Strowger mechanism 460 and comprises a wiper set, including the wipers 66|, 662, 666 and 664, and vertical, rotary and release magnets M161, M156 and M165, respectively, for controlling the movements of the carriage thereof, in the previously described manner. Also there are associated with the Strowger mechanism 660 a number of sets of switch springs S161, S136, S666,

Also associated with the Strowger S606, 8606 and8661 corresponding to the sets of switch springs B661, B666, S406, S466. B460 and S461, respectively. which are actuated in a similar manner. The minor switch 166 comprises a rotatable wiper 10| and an associated radially disposed contact bank 102 including a number of contacts adapted to terminate the control conductors C1II, C1|2 and C1I6, for a purpose more fully described subsequently. Also, the minor switch 166 includes rotary and release magnets M103 and M104, respectively, for controlling the movements of the wiper 16|, in the previously described manner.

Furthermore, the selector switch 166 comprises s. group of relays and their control and controlled circuits, this group of relays including a line relay R1| 6, a hold relay R120, a test relay R066, a busy relay R600, a switch-through relay R016 and a number of control relays R166, R140, R166, R100, R116, R106, R166, R666, R6|6, R626, R640 and R066. Also, a supervisory lamp L106 is individually associated with the selector switch 100 for a purpose more fully described subsequently. Furthermore, the selector switch 166 is directly inclutcd in the telegraph line 66|, as previously no Each of the printing mechanisms included at the central switching station C may be identical to the printing mechanism 466 which is preferably of the well-known Morkrum-Klcinschmidt type. 'Ihis printing mechanism includss a printing magnet M40I, connected to the line conductors C66| and C662 oi' a printing line, and an operating motor 402. The operating motor 402 is included in a control circuit comprising a battery 403 and a contact RA466, the latter contact being controlled by a start relay R464 connected to the control conductor C666 of the printing line, the line conductors C60| and C602 and the con- 4trol conductor C666 of the printing line being terminated at corresponding contact sets in tha contact banks of the Strowger mechanisms of the selector switches included in the central switching station C. Similarly, the conductors of the printing lines extending to the printing mecha nisms u1 and m are terminated et correspond-` ing contact sets in the contact banks of the Strowger mechanisms of the last-mentioned selector switches. The contact sets mentioned in each ofA the contact banks of the Btrowger mochanisms are arranged adjacent each other and in corresponding positions in the contact banks in order to accommodate hunting by the selector Y switches for an idle printing line. i

Each of the dial-transmitting-printing mechanisms included in the central switching station C may be identical to the mechanism |00, which is of the Morkrum-Kleinschmidt type, and comprises a dial mechanism |6| including cooperating contact springs, a key switch |61, a transmitting mechanism |62, and a printing mechanismy provided with a printing magnet PM|63. Also, this mechanism comprises an operating motor |64 included in an operating circuit including a battery |66 and a manually operable switch |66. The dial mechanism |6|, the key switch |61, the contacts of the transmitting mechanism |62 and the printing magnet PMI 63 are arranged in series circuit relationship and connected to conductors terminated by the respective tip and ring of the plug |66. y

Each of the dial-transmitting-printing mechanisms included in each of the terminal and wayside stations may be identical to the mechanisms 8|0 and 066 included in the station S, the mechanism 6|6 being of the Morkrum-Kleinschmidt type and including a dial mechanism 8| I, a key switch 8|4, a transmitting mechanism 8|2 and a printing mechanism provided with a printing magnet PM8 I3 arranged in series circuit relationship and directly included in the telegraph line erating motor 828 arranged in two parallel operating circuits, one of the operating circuits including the motor 828, a battery 828, and a manually operable switch 825; and the other operating circuit including the motor 828, the battery 826 and the contact RA82| of a start relay R820. The start relay R820 is provided with an energizing circuit which, when completed, includes the wiper 80| of the selector switch 800. Also a supervisory lamp L821v is connected across the terminals of the motor 828 in order to provide anindication of the .operating conditionof this motor.

Similarly, the mechanism 830 includes a dial mechanism 83|, a key switch 834, a transmitting mechanism 832, and a printing mechanismprovided with a printing magnet PM883 arranged 'in series circuit relationship and directly included in the telegraph line |02.` Also, the mechanism A830 comprises an operating motor 848 arranged in two parallel operating circuits, one of the operating circuits including the motor 848, a battery 846, and a manually operable switch 845; and the other operating circuit including themotor 848, the'battery 846, and the contact RA84| of a start relay R840. The start relay R840 is provided with an energizing circuit which, when l the double winding type", the relays Rl |0 and RI 40 so long as either the respective upper or lower winding thereof is maintained energized. The lower windings of the relays RI I0 and R|20 are arranged in series circuit relationship with the telegraph line |0|; the lower windings of the relays R|30 and R|40 are arranged in series circuit relationship with the loop circuit 30|; and the upperA windings of the relays R||0, R|20, R|30 and R|40 are arranged in an associated control network, in a manner more fully described subsequently.

The operation of the telegraph system and the connection and arrangement of the apparatus incorporated therein will best be understood from a consideration of the following description of the operation of the apparatus incorporated in the telegraph system to set up the different connections between the various stations.

Extending connections from the station C to the stations N or S or wayside stationspn the telegraph lines 101 or 102 A connection which is to beV extended from the central switching stationCto the terminal stations Also, the mechanism 8| 0 comprises an op- N or S may be routed thereto by way of either one of the telegraph lines |0| or |02; however, a v

connection which is to be extended from the cen.-

tral switching station C to a particular wayside station associated with the ytelegraph lines |0| or |02 must be routed over the particular. one of the telegraph lines |0| or |02 with which the wayside station is associated. For example, in order to extend a connection from thecentral switching station C to the terminal station S'by way of the telegraph line |0| or to a wayside station associatedwith the telegraph line |0|, the

-minal stations N and S extends from the posi-I tive terminal of battery in the terminal station N by way of the telegraph line 0|, the lower windings of the relays RI I0 and R|20 in the repeater K |00, RAI I, the jack |03 and the dial-transmitting printing mechanism 8| 0 to the negative terminal of battery in the selector switch 800 in the terminal station S. After the plug |05 is inserted into the jack |08 the circuit of the mechanism |60 is included in the above-traced circuit and the above-traced circuit then extends `from the positive terminal of battery in the terminal station N by way of the previously traced circuit Ito one switch spring of the jack |03 and from the negative terminal of battery in the selector r.switch 800 in the terminal station S by Way of the previously traced circuit to the other switch springof the jack |03, the switch springs of the jack |03 beingconnected together by way of a circuit including the tip of the plug |05, the contact springs of the dial mechanism |6|, the key switch |61, the contact springs of the transmitting mechanism |62, the winding of the printing magnet PMI63 and the ring of the plug |05 arranged in series circuit relationship. The operator at the centralswitching station C then operates the switch |66, thereby to complete the obvious circuit for operating the motor |64 of the mechanism |60, thereby to condition the mechanism |60 to transmit telegraphic impulses;

'I'he operator at the central stationC then operates the key |61 in order to move the switch springs thereof into disengagement, thereby to interrupt the circuit including the telegraph line |0| extending between the terminal stations N and S in order to insure that all of the selector switches included in the stations associated with the telegraph line |0| initially occupy their normal positions. The key switch |61 is then operated, after a predetermined time interval, to move the switch springs thereof'back into engagement at which time the apparatus associated with the telegraph line |0| 4is in condition to be responsive to a series of digits dialed at the dial mechanism |6|. The operator at the dial mechanism |6|, thereby to cause the contact springs thereof to interrupt the circuit including the telegraph line |0,| a predetermined number of times corresponding to the firstl digit dialed and to transmit a corresponding number of impulses over the telegraph line |0|. This series For exam- .central switching station C then operates the' responding to the iirst digit dialed. 'I'he operthe wipers carried by the carriages of the Strow` ator at the central switching station C then opcrates the dial mechanism |8| to transmit a second series of digits over the telegraph line |0|, thereby to cause the carriages of the Strowger mechanisms noted to be operated in the radial direction to the radial position of the contact set corresponding to the second digit dialed. At this time the wiper carried by the carriage-of the Strowger mechanism included in the selector switch 800 in the station S engages the contact terminatingthe conductor included in the circuit for energizing the start relay R820; and the wipers 804 and 808 engage the contacts terminating the shorting strap 805. On the other hand,

ger mechanisms of the selector switches included in the other stations associated with the telegraph line |0| engage corresponding contacts f which terminate no conductor. Accordingly, only the selector switch 800 is further operated to switch through. Upon switching through, the

selector switch 800 completes an obvious circuitA for energizing the start relay R820, operates to return an answer-back signal over the telegraph line |0|, and operates to connect the wipers 804 and 806 and the shorting strap in the series circuit including the telegraph line |0|.

Also, it is noted that the two digits 1dialed at the mechanism |6| are repeated by way of the repeater |00 to the loop circuit 80| extending between the repeater |00 and the selector switch 300 individually associated therewith. The exact manner in which the repeater |00 operates to repeat the two digits from the telegraph line |0| to the loop circuit 30| will be described in detail hereinafter. These two digits repeated to the selector switch 300 cause this selector switch to be operated, thereby to cause the carriage of the Strowger mechanism 480 to be moved in the vertical and radial directions to a position corresponding to the positions of the carriages of the other selector switches, included in the other stations associated with the telegraph line |0|. The exact manner in which the selector switch 800 is operated to move the carriage thereof in the vertical and radial directions is described in detail hereinafter.

When the selector switch 800 operates to return the answer-back signal over the telegraph line |0I, the repeater |00 operates, in a manner to be described hereinafter, to repeat the answerback signal to the loop circuit 30| extending between the repeater |00 and the selector switch 300. More particularly, the repeater causes the previously mentioned loop circuit to be interrupted for a predetermined time interval, thereby to cause the line relay R3|0 included in this loop circuit to restore. Upon restoring, the line relay R3|0 completes, at RA3l4, an obvious circuit for energizing the supervisory lamp L388, thereby yto indicate to the operator at the central switching station C that the printing mechanism at the called terminal station S has been seized. Shortly thereafter the hold relay R320 in the selector switch 300 restores, thereby to cause a circuit, traced hereinafter, for energizing the release magnet M355 to be completed in order to cause theselector switch 300 to be released and returned toits normal position. The exact manner in which the selector switch 80| is released is described indetail hereinafter.

' Similarly, the selector switches included in eachoi. the stations associated with the telegraph line i 0| are released when the answer-back signal is transmitted over the telegraph line lll by the selector switch 800. Shortly thereafter the selector switch |00 operates to terminate the return of the answer-back signal over the telegraph line 0| and to recomplete the' circuit including the telegraph line |0I extending between the terminal stations S and N. When the return of the answer-back signal over the telegraph line |l| is terminated, the repeater |00 operates to recomplete the loop circuit 30| extending between the repeater 00 and the selector switch 200, thereby to cause the line relay R8|0 to reoperate. Upon reoperating, the line relay RIII interrupts, at RASH, the above-mentioned circuit for energizing the supervisory lamp Ll", thereby to indicate to the operator at the central switching station C that the return of the answer-back signal over the telegraph line |0| has terminated.

The operator at the central switching station C then operates the dial mechanism IBI, thereby to transmit two additional series of impulses over the telegraph line |0| which are repeated by the repeater |00 to the loop circuit 30| in the previously mentioned manner. These two series of impulses constitute the two digits oi' a lockout number and are effective to cause the selector switch 300 and each 'of the selector switches in the stations associated with the telegraph line 0| to be operated to a lockout position. 'Ihe exact manner in which the selector switch 300 is operated to a lockout position is described in detail hereinafter. When the selector switches noted are operated to their lockout positions, they are rendered inoperative. Accordingly, the Strowger mechanisms therein do not follow the telegraphic impulses which are subsequently transmitted over the telegraph line I0|.

When the previously mentioned circuit for energizing the start relay R820 is completed, the latter relay operates to complete the previously mentioned circuit for operating the motor 828 and for illuminating the supervisory lamp 1.821, respectively. Upen operating, `the motor 828 renders the mechanism 8|0 in'condition to receive and print telegraphic impulses transmitted thereto. The illumination of the supervisory lamp L821indicates the operating condition of the operating motor 828 to the operator at the station S. Also, upon switching through, the selector switch 800 interrupts the path for applying negative battery potential to the telegraph line |0| incoming to the selector switch 800 and the path for applying positive battery potential to the line outgoing from the selector switch 800 to the mechanism 8|0 and completes a connection between the telegraph line 0| incoming thereto and the last-mentioned line outgoing therefrom.

At this time the circuit extending from positive battery potentialin the station N is extended by way of the selector switch 800, the dial mechanism 8| I, the key switch 8| 4, the contact springs of the transmitting mechanism 8|2, the winding of the printing magnet PM8|3 and the selector switch 800 to the telegraph line |0| connected to the negative terminal of battery in the station S.

At this time an established connection is completed by way of the telegraph line |0| between the mechanism |60 in the central switching staciated with the repeater I occupy locked out positions. Accordingly, only the vmechanism l|0 is' adapted to follow the telegraphic impulses transmitted from the transmitting mechanism |62 included in the mechanism |60 in the central switching station C. The operator at the central switching station 'C then'operates the transmitting mechanism |62, thereby to transmit tele-l graphic impulses over the circuit including the telegraph line IOI; and the printing magnet, PM6|3 of the mechanism 8I0 included in the station S follows the telegraphic impulses transmitted thereto and operates the associated printer included in the mechanism 0I0 to print the telegraphic message.

As previously noted, the dialed impulses transmitted over the telegraph line |0I are repeated by the repeater |00 to the loop circuit 30| extending between the repeater |00 and the selector switch l300. 'Ihe lower windings of the relays RI I0 and R|20 are included in series circuitrelationship with the telegraph line IOI; and the lower windings of the relays RI30 and RI40 are included in series circuit relationship with the loop circuit 30|, as previously noted. More specifically, the circuit including the telegraph line |0Iextends from one portion of the telegraph line |0I by way of the lower winding of RI I0, the lower winding of R|20 and RAI I I to another portion of the telegraph line IOI, positive and negative battery potentials appearing upon the respective portions of the telegraph line I0| as previously traced.

.The above-mentioned loop circuit 30| extends from the positive terminal of battery by way of the resistor 435, RC4I5, RA4I4, RA432, RA412, RC413, RA422, C3I0, the winding of the line relay R3I0, C303, RAI4I, the lower winding of RI30, the lower winding of RI40, C302, RA43I, RA41I, RA42I, RA4II, RC4I2 and the resistor 434 to the negative terminal of battery. Thus, the lower windings of the relays RI I0 and RI 20 l are normally energized in series over the circuit including the telegraph line IOI; and the lower windings of the relays RI30 and RI40 are normally energized in series over the loop circuit 30|. 'I'he upper winding of the relay RI I0 is provided with a normally completed energizing circuit extending from the positive terminal of battery by way of the resistor |50, the upper winding of RI I0 and the resistor I5I to the negative terminal of battery. Also, a path is provided for short-cir-` cuiting the upper winding of the relay RI I0 which extends, when completed, from the positive terminal of battery by way of RAI3I, RCI32, the upper winding of RI I0 and the resistor R|50 to the positive terminal of battery. 'Ihe upper winding of the relay RI40 is provided with a normally completed energizing circuit extending from the positive terminal of battery by way of the resistor |51, the upper-winding of RI40 and the resistor |56 to the negative terminal of -battery. Also, a path is provided for short-circuiting the upper Winding of the relay RI40 which extends, when '-ompleted, from the positive terminal of battery by way of RAI2I, RCI22, the upper winding of RI40 and the resistor I 51 to the positive terminal of battery. The upper winding minal of battery by way of the resistor |52, the upper winding of R| and the resistor |53 to the negativeterminal of battery, and the normally completed short-circuiting path extending from 4the positive terminal of battery by way of RAI2 I, RC|23 and the resistor |54 to the negative terminal of battery. 'Ihe upper winding of the relay R| is provided with an energizing circuit around which a short-circuiting path is normally completed, the energizing circuit extending, when completed, from the positive terminal of battery by way of the resistor |55', the upper winding of RI30 and the resistor I 54 to the negative terminal of battery, and the ,normally completed shortcircuiting path extending from the positive terminal of battery by way of RAIN', RCI33 and the resistor |53 to the negative terminal of battery.

When the previously traced circuit vincluding the telegraph line IOI is interrupted at the beginning of the iir'st impulse transmitted thereover, the above-traced circuit for energizingin series the lower windings of the relays RI I0 andy-R|20 is interrupted. The relay RI I0 remains in its operated position due to the fact that the previously traced circuit for energizing the upper winding thereof is retained completed, the upper winding of the relay RI I0 producing a magnetic ilux predominating overI that produced by the lower winding thereof, as previously noted. However. the relay R|20 restores. Upon restoring, the relay R|20 interruptavat RAI2I and RCI23, a point in the previously traced path for short-circuiting the upper winding of the relay RI30, thereby to cause the previously traced circuit for energizing the upper'winding thereof to be completed. Also, upon restoring, the relay R|20 completes, at RAI2| and RCI22, the previously traced path for short-circuiting the upper winding of the relay RI40. When the upper winding of the relay RI40 is short-circuited, the latter relay restores due to the fact that the upper winding thereof produces a magnetic flux which predominates over that produced by the lower winding thereof. Upon restoring, the relay RI40 interrupts, at RAMI, a point in the previously traced loop circuit, thereby to cause the circuit for energizing in series the lower windings of the 'relays RI30 and RI40 to be interrupted. It is noted that the relay RI30 does not restore when the circuit for energizing the lower `winding thereof is interrupted due to the fact that the previously traced circuit for energizing the upper winding thereof is completed when the relayR|20 restores.

When the previously mentioned loop circuit 30| is interrupted, the line relay R3|0 restores. Upon restoring, the line relay R3| 0 interrupts, at RA3I| and RC3I2, an obvious circuit for energizing the hold relay R320. The latter relay, being of the slow-to-release type, does not immediately restore.v Also, upon restoring, the line relay R3I0 completes, at RA3II and RC3I3, a circuit for energizing in series the control relay R330 and the vertical magnet'M351,g this circuit being prepared, at RA324 and R032 5, due to the operated condition of the hold relay R320. 'I'he above-mentioned series circuit extends from the positive terminal of battery at RA3|| by way of RC3I3, RA324, RC325, the switch springs S366 and S364 of the s'et of switch springs S361, the .winding of R330 and the winding of M351 to the negative terminal of battery. When energized over the above-traced circuit, the relay R330 operates to prepare, at RA332 and RC333, an alternative circuit for energizing the winding thereof in series with the winding o'i the vertical magnet M301; and to complete, at RA33I, a circuit for energizing the control relay R340, the latter circuit extending from the positive terminal of battery by way of RA33I and the winding of R340 to the negative terminal oi' battery. Also, when energized over the previously traced circuit, the vertical magnet M351 operates to move the carriage of the Strowger mechanism 400 one step in the vertical direction at which time the sets of switch springs S301, S330 and S400 are actuated. More particularly, the switch springs S304 and S030 and the switch springs S300 and S300 of the set of switch springs S301 are actuated into disengagement and into engagement, respectively. When the switch springs S304 and S300 are actuated into disengagement, the previously traced circuit for energizing in series the winding oi.' the relay R330 and the winding of the vertical magnet M351 is interrupted; and when the switch springs S305 andvS300 are actuated into engagement, the previously mentioned alternative circuit i'or energizing in series the winding of the relay R330 and the winding oi the vertical magnet M351 is completed. 'Ihe last-mentioned alternative circuit extends from the positive terminal of battery at RA3I I by way of RC3I3, RA324, M005, S355, S305, RA332, RC333, the winding of R330 and the winding of M351 to the negative terminal of battery. More particularly, the set of switch springs S330 are actuated into engagement, thereby to prepare a circuit. traced hereinafter, for energizing the release magnet M355; and the switch springs S403 are actuated into engagement, thereby to prepare a circuit, traced hereinafter, for energizing the lower winding oi! the switch-through relay R410.

Upon operating, the control relay R340 completes, at RA34I, a holding circuit for energizing the winding thereof extending from the positive terminal of battery by way of RA34I and the winding of R340 to the negative terminal of battery. Also, upon operating, the control relay R340 completes, at RA342, a circuit for energiz ing the control relay R400, this circuit extending from the positive terminal of battery at RA342 by way of C3I4, RA4I1, RC4I0 and the winding oi.' R400 to the negative terminal of battery. When energized over the above-traced circuit, the relay R400 operates to interrupt, at RA401 and RC409, a point in a circuit, traced hereinafter, i'or energizing the control relay R4I0; and to complete, at RA401 and RC400, a circuit for applying positive battery potential to the control conductor C530 of the trunk line 535 extending into the multiple 530, the latter path extending from the positive terminal of battery by way of RA342, C3I4, RA4I1, RC4I9, RC400 and RA401 to the control conductor C530. This application of positive battery potential marks, by way of the trunk line 535 and the multiple 530, the contacts in the contact banks of the Strowger mechanisms included in the selector switches 520 and 100 terminating the control conductor C530 with positive battery potential, thereby to mark the trunk line 535 and the selector switch 300 individually associated therewith as busy to the selector switches 520 and 100. Also, upon operating, the relay R340 interrupts, at RA343 and H0345, a circuit, traced hereinafter, for energizing the release magnet M355; and completes, at RA343 and RC344, a circuit for energizing the control relay R300. The last-mentioned circuit extends from the positive terminal of battery by Way o! RAIZI, RC020, RAMI, H0313, RA343,

aai 1,027

RC344, the winding of R000 and the resistor 330 to the negative terminal of battery, the control relay R310 being operated at this time. vShortly after the lrelay R300 is energized over the previously traced circuit. the latter relay, being of the slow-to-opera'te` type, operata to initiate a timins operation, in a manner more fully described subsequently.

Also. upon operating. the relay R330 completes, at RA330, a circuit for energizing the control reg lay R310, this circuit extending from the positive terminal o! battery by way of the set oi switch springs S400, C3I5, RA330, C323 and the winding of R310 to the negative terminal oi battery. Upon operating, the relay R310 completes, at RA310, a holding circuit for energizing the winding thereof, this lcircuit extending from the positive terminal of battery by way of the set oi switch springs B400, RA425, RA434, RA402, C32I, RA315 and the winding ot R310 to the negative terminal oi' battery. Also. upon operating, the relay R310 prepares, at RA314, a point in a circuit, traced hereinai'ter, for energizing in series the rotary magnet M350 and the, control relay R300.

Continuing now with the operation of the repeater I00, when the circuit including the telegraph line IOI is again completed at the end of the rst impulse, the previously traced circuit for energizing in series the lower windings of the relays RI I0 and RI20 is recompleted. When this series 'circuit is recompleted, the relay RI I0 is retained in its operated position and the relay RI is operated. Upon operating, the relay RI20 interrupts, at RAIZI and RCI22, the previously traced path for short-circuiting the upper winding of the relay RI40, thereby to cause the previously traced circuit for energizing the upper winding of the relay RI40 to be completed. When the upper winding ot the relay RI40 is then energized, this relay operates to complete, at RAI 4I, the previously traced loop circuit thereby to complete the previously traced series circuit for energizing the lower windings of the relays RI and RI30. When this series circuit is completed, the relays RI30 and RI40 are retained in their operated positions. Finally, upon operating, the relay RI20 completes, at RAIZI and RCI23, the previously traced path for short-circuiting the upper winding of the relay RI30, the relay RI 30 being retained in its operated condition at this time due to the completed circuit for energizing the lower winding thereof.

When the loop circuit 30| is recompleted, the previously traced circuit for energizing the line relay R3I0 is recompleted, thereby to cause the latter relay to reoperate. Upon reoperating, the relay R3'i0 completes, at RA3II and RC3I2, the previously mentioned circuit for energizing the hold relay R320; and interrupts. at RA3II and RC3I3, the previously traced alternative circuit for energizing in series the control relay R330 and the vertical magnet M351. It will be understood that the impulses comprising the iirst sexies of impulses are transmitted over the circuit including the telegraph line IOI at a relatively fast rate of between ten and fourteen impulses per second. Accordingly, the repeater |00 is repeatedly operated to cause the series of impulses to be'repeated to theloop circuit 30| in the previously described manner. Thus, the line relay R3I0 follows the series of impulses comprising the ilrst digit dialed, thereby to cause the control relays R320 and R330 to be alternatively and repeatedly energized. The last two `mentioned las operated during the ilrst series of impulse com ,per set of the stromen mechamsnrfnlinfcluded-f Ik ith@ SQIQQOM SWzitchcIN-foccupiesi rvertical` wie@ digitfdlled. and.4 Atheline relay :R31 0% isreoperated A AISO.. ShQrtlyfIOllowing-the-:conclusion "off the rst At rnebegmnmg-orrne nrseimpmse comprising from,` thewpositive terminal sof` battery byy way of tive terminalof fbatterwiwhen energized overly* f the-A` above-mentioned. circuit, the Arelay R360,

operates-toccomplete, at RA362, an alternative circuit for lenergizingsthe winding thereof iny series with thefwindingl of the rotary magnet M356, this alternative circuit being substantially the same as the previously traced circuit and including a shunt path provided by the contact RA362 aroundthe contact RA314 of the control relay R310. Also, upon operating, the relaylR360 completes, at RA36|, a circuit for energizing the control relay R460, this circuit extending vfrom the positive terminal of battery by way of RA36I, C320 and the winding of R460 to the negative terminal of battery. When energized over the previously traced circuit, the relay R460 operates J to interrupt, at RA462, a Vpoint in the previously ing, the relay R310 interrupts, at RA314, a point r in the original circuit for energizing in series the control relayR360 and the rotary magnet M356; and interrupts, atRA315, a further point in the holding circuit for energizing the winding thereof. Also, upon restoring, the control relay R310 interrupts, at RA31| and RC313, the previously traced circuit for energizing the control relay R380, ,thereby to cause the latter rrelay to restore and arrest the previously mentioned timing operation. Furthermore, the control relay R310 completes, at RA31| and RC312, the circuit for energizing the release magnetM394, this circuit extending from the positive terminal of battery by way of RA32 I, RC323, RA31I, RC312, the set'of switch springs S395 and the winding of M394 to the negative terminal of battery, the set of switch springs S395 being actuated into engagement at this4 time, as will be explained in detail hereinafter. When energized over the previously traced circuit, the release magnet M394 operates to release the'wiper 39| of the minor switch 390, thereby to cause the wiper 39| to be returned to its normal position. Also, upon operating, the relay R460 interrupts, at

:id ,isf-,associaten-twitnia; 1eve11 in the associatedacoptact y,bankscorresponding to 7the first Y digit Ldialedsaathe monrroltrelay Ram; being of mei s1w`tfre1e5-=typezrestores itofiprepgre, at "Rem.andman,.mezpreviouslymentiend circutfforfienersizingr insel-ies vthe feontrcrrelay i pulses comprising ytlie vsec'or'id;` di hfseeonddiglt dialed;ther-repeater'|00operatesi'fltiine the relay-iR 3|0""oprates.

;uthe previouslyudescribed 'manner in order tozf cause the; loop .circuitt30 Lto4 beiinterrupted,` there` 5 ',byrto@ cause the.flineffrelay:` R3 I 0 to restore. YUpon :'fmentioneif nalterna .VandzRG3If3'thevpreviously mentioned circuit for 4energizing. in series the icontr'ol' relay R360 and :fthe rotary 1 magnet M356, this circuitV` extending mm, a point in a circuit, traced nifr, rela R436;.Rep%1es, at

stores, itiriterrupts; at lanni and RClz, the previously mentioned circuit for 'energizing the g5 hold'relay R320, and completes, vatJRA3|| and RC3| 3, the previously lmentioned' alternative cirfrfcuit for .energizing .in series' thecontrol relay R360 and tne rotarymagnet M1356.- As pre- Y viousiy noted, the line relay R310, operates` and 30 v restores at' a' relatively fast' rate, thereby to cause the hola relay R320 and the control relayrR360 to be alternatively and repeatedly energized. AThe l two last-mentionedrelays, being of the slow-torelease type, remain operated during the series 35 of impulsesv comprising the second digit. Each timevthe rotary magnet M356 is energized, it op f crates to move the carriage of the Strowger mechanism 460 included in the selector switch 300 one step in the radial direction.

yAt the` conclusion of the second digit dialed,

the wiper set carried by the carriage of the Strowger mechanism 480 occupies a radial position corresponding to the second digit dialed.

Shortly following'the conclusion of the second digit dialed, the control relay R360, being of the slow-to-release type, restores to interrupt, at RA362, a point in the alternative circuit for energizing the winding thereof in series with the winding of the rotary magnet M356, thereby to 50 prevent further operation of the rotary magnet M356 and consequently to arrest further movement of the carriage of the Strowger mechanism 480 in the radial direction. Also, upon restoring,

the relay R360 interrupts, at RA36I, the pre- 55 viously traced circuit for energizing the control relay R460. As previously noted, in the present instance no conductor 'is terminated by the contact set lengaged by the wiper set of the Strowger mechanism 480 when the. previously men- 00 tioned two digits are dialed. Accordingly, the wiper 483 of the wiper set of the Strowger mechanisrn 430 engages a contact having no potential thereon. Hence, the test relay R450 is not operated and shortly after the controlrelay R360 05- switch 300 occurs at this time until the repeater 70 |00 operates to repeat the answer-back signal transmitted over the circuit including the telegraph line |0| to the loop circuit 30|.

When the selector switch 800 operates 4to transmit the answer-back signal over the circuit 16 ithe previously I0 interval, thereby to cause the line relay R3I0 to` restore and cause the hold relay R320 to restore. Upon restoring, the hold relay R320 completes, at RA324 and RC3, a circuit for energizing the release magnet M355, this circuit extending from the positive terminal of battery by way of RA!! I RC3I3, RA324, RC326, C3!1, RA413, C3I3, the set ci' switch springs S336 and the winding of M355 to the negative terminal of battery.l When energized over the above-traced circuit, the release magnet M355 operates to complete, at MA355, a holding circuit for energizing the winding thereof, this holding circuit extending from the positive terminal o! battery by way of MA355, the set of switch springs S336 and the winding ot M355 to the negative terminal of battery. Also. upon operating, the release magnet M355 releases the carriage oi' the Strowger mechanism 430 included in the selector switch 333, thereby to cause the carriage to return to its normal position. When the carriage of the Strowger mechanism 433 included in the selector switch 300 is returned to its normal position, the sets of switch springs S433 and S336 are actuated into disengagement; while the switch springs S365 and S366 and the switch springs S364 and S366 of the set of switch springs S361 are actuated respectively into disengagement and engagement. When the set of switch spring S433 is actuated into disengagement, a further point in the circuit for energizing the lower winding of the switch-through relay R410 is interrupted; when the set of switch springs S336 ,is actuated into disengagement. the previously traced holding circuit for energizing the winding of the release magnet M355 is interrupted, thereby to cause the release magnet M355 to restore and interrupt,at MA355, a'

further point in the previously traced holding circuit for energizing the winding thereoi; when the switch springs S365 and S366 of the set of switch springs S361 are actuated into disengagement, a further point in the circuit for energizing in series the control relay R360 and the rotary magnet M356 is Interrupted; and when the switch springs S364 and S366 of the set of switch springs S361 are actuated Into engagement, a point in the previously traced circuit for energizing in series the control relay R330 and the vertical magnet M351 is prepared.

Also, upon restoring, the hold relay R320 interrupts, at RA32! and RC323, a further point in the previously traced circuit for energizing the release magnet M334 and completes, at RA3!! and RC3!!, an alternative circuit for energizing the control relay R330, this circuit extending from the positive terminal of battery by way of RA3! I RC322, RA343, RC344, the winding of R360 and the resistor 366 to the negative terminal of battery. When energized over the above-traced circuit, the relay R330 operates shortly thereafter, this relay being of the slow-to-operate type, to initiate the previously mentioned timing operation. More particularly, the control relay R360 interrupts, at RA33! and RC334, a point in the previously mentioned circuit for energizing the rotary magnet M333; interrupts, at RC332 and RC333, an obvious path for short-circuiting the winding of the control relay R335; and completes, at RA33| and RC33Z, an obvious circuit for energizing the winding of the control relay R365, thereby to cause the latter relay to operate shortly the previously mentioned circuit for energizing the Winding of the control relay R335; to complete, at R033! and RC333, the previously mentioned path for short-circuiting the winding of the relay R335; and to complete, at RA33! and RC334, the previously mentioned circuit for energizing the rotary magnet M333. The latter circuit extends from the positive terminal of battery by way of RA33I, RC3, RA331 and the winding ot M333 to the negative terminal of battery. When energized over the above-traced circuit, the rotary magnet M333 operates to drive the wiper 33! of the minor switch 333 away from its normal position one step in the clockwise direction. When the wiper 33| of the vminor switch 333 is moved away from its normal position, the switch springs S335 are actuated into engagement, thereby to prepare the previously traced circuit for energizing the release magnet M334. When the previously mentioned path for short-circuiting the winding of the relay R335 is completed, the latter relay restores to interrupt, at RA336, the previously traced path for short-circuiting the winding of the relay R330 and to interrupt, at RA331, a point in the previously traced circuit for energizing the rotary magnet M333. When the previously traced path for short-circuiting the winding of the relay R330 is interrupted, the latter relay reoperates to recomplete, at RA33! and RC33!, the previously mentioned circuit for energizing the relay R335, thereby to cause the latter relay to reoperate shortly thereafter. The control relays R330 and R335 interact, in the above-described manner, in order to cause the rotary magnet M333 to be repeatedly energized. When the wiper 33! of the minor switch 330 is rotated into engagement with the contact in the associated contact bank 33! terminating the control conductor C3! 2, a circuit is completed for energizing the control relay-R4!0, this circuit extending from the positive terminal of battery by way of RA34I, C322, the wiper 33|, the contact in the associated contact bank 332 terminating the control conductor C3! 2,C3!! and the winding of R420 to the negative terminal `of battery. When energized over the previously traced circuit, the relay R420 operates to complete, at RA423, a holding circuit for energizing the winding thereof, this circuit extending from the positive terminal of battery by way of RA342, C3I4, RAI!! and the winding ofR423 to the negative terminal of battery. Also, upon' operatinggthe relay R420 interrupts, at RA42! and at RA422, additional points in the loop circuit When the wiper 33! of the rotary switch 333 is driven into engagement with the contact in the associated contact bank terminating the control conductor C3|3, a path is completed for short-circuiting the winding of the control relay R340, this path extending from one terminal of the winding of R343 by way of C322, the wiper 33! and contact in the associated contact bank terminating'the control conductor C3|3 and C3!3 to the other terminal of the winding of R340. When the previously 

